Current technology makes it possible to produce sensors in which the integration duration of the electric charges generated by light in the pixels can vary between a few hundreds of nanoseconds and twenty milliseconds (or more if a reduction of the rate of the images to less than 50 images per second is accepted). It is difficult to reduce the integration duration below 100 or 200 nanoseconds; the reason is that the sequencing of the operation of a sensor is established by synchronous logic circuits; it would not be possible to reduce the durations of the synchronous signals below about one hundred nanoseconds securely.
There could, however, be a need to take images with an even shorter integration duration. This may be the case, for example, if the intention is to use the sensor, by combining it with a pulsed light source, in order to measure distances or to take an image of a scene at a given distance. This measurement or control of the distance of the observed scene is based on knowledge of the time of flight of the light between the source and the sensor after reflection from a point in the scene being observed. It therefore relies at least partly on good synchronization between the moment when a light pulse is sent and the moment when the charges generated by the return of this light pulse onto the sensor are integrated. The precision of the measurement or of the control of the distance may depend in particular on the integration duration of the charges generated by the light pulse. Typically, a duration of 100 nanoseconds corresponds to a distance of 30 meters travelled by the light, but there may be a desire to benefit from a shorter integration duration in order to improve the precision of the measurement or of the distance control.